Morphology control of laser-induced dandelion-like crystals of sodium acetate through the addition of acidic polymers

Abstract

Crystal growth speeds, crystal sizes and the morphology of sodium acetate (CH3COONa) crystals in the presence of polymaleic acid and polyacrylic acid with different concentrations were investigated in supersaturated solutions of sodium acetate. The technique of non-photochemical laser-induced nucleation (NPLIN) was used to produce initial crystallites of anhydrous CH3COONa. The anhydrous CH3COONa crystal growth in solution after laser irradiation resembled the formation of dandelion seed heads. Even though NPLIN could offer temporal–spatial control of crystal nucleation without the addition of acidic polymers, the crystal growth rates were heterogeneous for crystallites along the laser pathway, which led to irregular crystalline sizes and morphologies. Here, a controllable approach from crystal nucleation to crystal growth has been designed through the addition of acidic polymers in the laser-induced growth of anhydrous CH3COONa crystals. In the presence of an acidic polymer, both the crystal growth and the morphological modification were controlled from tuft-shaped crystals to dandelion-like crystals. As bulk solid thicknesses and crystal growth speeds can be modified by different mass fractions of acidic polymer, a mathematical model was established to analyse the dynamics of crystal growth under the effect of acidic polymers. The model reproduces remarkably well the experimental trend and predicts experimental results. The changes in supersaturation and the number of nuclei through the addition of acidic polymers were analysed to investigate the underlying mechanism of morphological difference.